I think you have the makings of a great story, but for a first chapter there's a lot going on. Try slowing down and adding more detail about the characters; Ambers past - why is she coming to Hogwarts, The train journey - who does she meet, The sorting and The feast. Slow it down and stretch it across more chapters. I really liked it and with a few alterations I think it will be even better! Keep writing! x